1 November 19, 2015 1 November 19, 2015November 19, 2015November 19, 2015 Azusa, CA Sheldon X. Liang Ph. D. Computer Science at Azusa Pacific University

1

April 20, 20231

April 20, 2023April 20, 2023 Azusa, CAAzusa, CA

Sheldon X. Liang Ph. D.

Computer Science at Computer Science at Azusa Pacific UniversityAzusa Pacific University

Azusa Pacific University, Azusa, CA 91702, Tel: (800) 825-5278 Department of Computer Science, http://www.apu.edu/clas/computerscience/

CS400 Compiler ConstructionCS400 Compiler Construction

2

April 20, 20232


CS@APU: CS400 Compiler ConstructionCS@APU: CS400 Compiler Construction

Keep in mind following questionsKeep in mind following questions

• Syntax-Directed Translation– What is added into a grammar?– What is an attribute?– How to use an attribute?

• Why we need attributes– How to parse by a grammar?– What inspires you?

• What is your reflection– Like it, why?– Hate it, why?

3

• Uses a CF grammar to specify the syntactic structure of the language

• AND associates a set of attributes with the terminals and nonterminals of the grammar

• AND associates with each production a set of semantic rules to compute values of attributes

• A parse tree is traversed and semantic rules applied: after the computations are completed the attributes contain the translated form of the input

April 20, 20233



Syntax-Directed TranslationSyntax-Directed Translation

http://www.apu.edu/clas/computerscience/

4

• An attribute is said to be …– synthesized if its value at a parse-tree node is

determined from the attribute values at the children of the node

– inherited if its value at a parse-tree node is determined by the parent (by enforcing the parent’s semantic rules)

April 20, 20234



Synthesized and Inherited AttributesSynthesized and Inherited Attributes


5

expr expr1 + termexpr expr1 - termexpr termterm 0term 1…term 9

expr.t := expr1.t // term.t // “+”expr.t := expr1.t // term.t // “-”expr.t := term.tterm.t := “0”term.t := “1”…term.t := “9”

Production Semantic Rule

String concat operator

April 20, 20235



Example Attributes GrammarExample Attributes Grammar


6

expr.t = “95-2+”

term.t = “2”

9 - 5 + 2

expr.t = “95-”

expr.t = “9” term.t = “5”

term.t = “9”

April 20, 20236



Example Annotated Parse TreeExample Annotated Parse Tree


7

procedure visit(n : node);begin for each child m of n, from left to right do visit(m); evaluate semantic rules at node nend

April 20, 20237



Depth-First TraversalsDepth-First Traversals


8

expr.t = “95-2+”

term.t = “2”

9 - 5 + 2

expr.t = “95-”

expr.t = “9” term.t = “5”

term.t = “9”

Note: all attributes areof the synthesized type

April 20, 20238



Depth-First Traversals (Example)Depth-First Traversals (Example)


9

• A translation scheme is a CF grammar embedded with semantic actions

rest + term { print(“+”) } rest

Embeddedsemantic action rest

term rest+ { print(“+”) }

April 20, 20239



Translation SchemesTranslation Schemes

Here “print” means generation of code

10

expr expr + termexpr expr - termexpr termterm 0term 1…term 9

{ print(“+”) }{ print(“-”) }

{ print(“0”) }{ print(“1”) }…{ print(“9”) }

April 20, 202310



Example Translation SchemeExample Translation Scheme

Syntax-directed:

Syntax (rules) that direct action to take

11

expr

term

9

-

5

+

2

expr

expr term

term

{ print(“-”) }

{ print(“+”) }

{ print(“9”) }

{ print(“5”) }

{ print(“2”) }

Translates 9-5+2 into postfix 95-2+

April 20, 202311



Example Translation SchemeExample Translation Scheme

12

April 20, 202312



Got it with following questionsGot it with following questions

• Syntax-directed Translation– What is added in to a grammar?– What is an attribute?– How to use an attribute?

• Why we need attributes– How to parse by a grammar?– What inspires you?

• What is your reflection– Like it, why?– Hate it, why?

13

Thank you very much!

Questions?

April 20, 202313



Syntax-Directed TranslationSyntax-Directed Translation

Documents

1 November 19, 2015 1 November 19, 2015November 19, 2015November 19, 2015 Azusa, CA Sheldon X. Liang Ph. D. Computer Science at Azusa Pacific University